金属套管对井中电磁场特性影响的有限元分析

在套管井中测量地层电阻率等信息必然会受到套管参数变化的影响。利用有限元数值方法对建立的非均质套管井低频电场模型进行了数值 分析,主要研究了套管的电阻率、磁导率、厚度及套管半径等对井中电磁场特性的影响。研究结果表明，接收电动势随套管电阻率的增大而逐渐 增大,当电阻率增大到一定程度时,接收电动势曲线趋于水平;随着套管相对磁导率增大接收电动势逐渐减小;随着套管厚度的增大接收电动势逐 渐减小,且近似呈线性变化;接收电动势幅度随着套管半径的增大先逐渐减小,后又逐渐增大,接收电动势相位随着套管半径的增大而逐渐增大,在 半对数坐标系下,近似呈线性变化。

Finite element analysis for the effect of metal casing on electromagnetic field in cased borehole

Measuring the formation resistivity in the cased hole would be affected by the parameter variation of metal casing,which must be corrected.Therefore,the low-frequency electromagnetic field in the inhomogeneous model of casing borehole was analyzed by finite element numerical simulation method,which was emphasized on the effect of resistivity,magnetic inductivity,thickness and radius of casing on electromagnetic field in cased borehole.The results show that the amplitude and phase of the received electromotive force (EMF) strengthen versus the increase of resistivity,when the resistivity reaches to some degree, the curve of EMF approximates to horizontal.Along with the increase of the thickness of the metal casing,the EMF gradually decreases and almost linearized.Along with the increase of radius of metal casing,the amplitude of EMF firstly gradually decreases and then gradually increases;the phase of EMF gradually increases and nearly linearized in the semi-logarithmic coordinates.